docs: def addPolicyURI(self, policy_uri):
          """Add a authentication policy to this response
  
          This method is intended to be used by the provider to add a
          policy that the provider conformed to when authenticating the user.
  
          @param policy_uri: The identifier for the preferred type of
              authentication.
          @see: http://openid.net/specs/openid-provider-authentication-policy-extension-1_0-01.html#auth_policies
          """
          if policy_uri == AUTH_NONE:
              raise RuntimeError(
                  'To send no policies, do not set any on the response.')
  
          if policy_uri not in self.auth_policies:
              self.auth_policies.append(policy_uri)